1. Field of The Invention
The field of art to which this invention pertains is the solid bed adsorptive separation of fatty acids. More specifically the invention relates to a process for separating saturated fatty acids which process employs an adsorbent comprising particular polymers which selectively adsorb one fatty acid from a feed mixture containing more than one fatty acid.
2. Background Information
It is known in the separation art that certain crystalline aluminosilicates can be used to separate certain esters of fatty acids from mixtures thereof. For example, in U.S. Pat. Nos. 4,048,205, 4,049,688 and 4,066,677, there are claimed processes for the separation of esters of fatty acids of various degrees of unsaturation from mixtures of esters of saturated and unsaturated fatty acids. These processes use adsorbents comprising an X or a Y zeolite containing a selected cation at the exchangeable cationic sites.
The use of crystalline silica for the separation of a fatty acid from a rosin acid is disclosed in U.S. Pat. No. 4,404,145 to Cleary et al. That patent also teaches the use of a displacement fluid having a minimum desired polarity index, i.e., at least 3.5. The hypothesis stated in U.S. Pat. No. 4,404,145 to Cleary et al. as to the unique suitability of its process for its claimed separation was that the silicalite pores were of a size and shape that enabled the silicalite to function as a molecular sieve, i.e., accept the molecules of fatty acids into its channels or internal structure, while rejecting the molecules of rosin acids.
The adsorptive separation of saturated fatty acids of different chain lengths from each other was disclosed in U.S. Pat. No. 4,353,839 to Cleary et al. The adsorbent used in the process of that patent was a hydrophobic insoluble crosslinked polystyrene polymer, and the desorbent a mixture of dimethylformamide and water.
U.S. Pat. No. 4,444,986 to Dessau discloses the use of a high silica zeolite for the separation of compounds of the same homologous series, including acid substituents of hydrocarbons, with the separation occurring in the presence of a solvent, including a polar solvent.
The present invention is based on the discovery that crystalline silica is highly suitable as an adsorbent for the separation process of this invention in that it exhibits relative selectivity for a long chain saturated fatty acid with respect to a shorter chain saturated fatty acid when used with an appropriate desorbent.